arXiv subjects

L. Braicovich

Publications and source records attributed to L. Braicovich.

42 records · Page 3Linked to original sources

arXiv2009

Orbital occupation, atomic moments and magnetic ordering at interfaces of manganite thin films

We have performed x-ray linear and circular magnetic dichroism experiments at the Mn L2,3-edge of the La0.7Sr0.3MnO3 ultra thin films. Our measurements show that the antiferromagnetic (AF) insulating phase is stabilized by the interfacial rearrangement of the Mn 3d orbitals, despite the relevant magnetostriction anisotropic effect on the double-exchange ferromagnetic (FM) metallic phase. As a consequence, the Mn atomic magnetic moment orientation and how it reacts to strain differ in the FM and AF phases. In some cases a FM insulating (FMI) phase adds to the AF and FM. Its peculiar magnetic properties include in-plane magnetic anisotropy and partial release of the orbital moment quenching. Nevertheless the FMI phase appears little coupled to the other ones.

cond-mat.str-el↗

arXiv2009

Resonant X-rays at the Cu L-edge as a momentum dependent probe of the magnetic excitation spectrum in cuprates

We show that, contrary to common lore, in resonant inelastic x-ray scattering (RIXS) at the copper L- and M-edge direct spin-flip scattering is in principle allowed. We demonstrate how this possibility can be exploited to probe the momentum dependent magnetic properties of cuprates such as the high Tc superconductors and compute in detail the relevant local and momentum dependent magnetic scattering amplitudes, which we compare to the elastic and $dd$-excitation scattering intensities. For cuprates these results put RIXS as a technique on the same footing as neutron scattering.

cond-mat.str-el↗

arXiv2009

Collective spin excitations in a quantum spin ladder probed by high-resolution Resonant Inelastic X-ray Scattering

We investigate magnetic excitations in the spin-ladder compound Sr$_{14}$Cu$_{24}$O$_{41}$ using high-resolution Cu $L_3$-edge Resonant Inelastic X-ray Scattering (RIXS). Our findings demonstrate that RIXS couples to collective spin excitations from a quantum spin-liquid ground state. In contrast to Inelastic Neutron Scattering (INS), the RIXS cross section changes only moderately over the entire Brillouin Zone (BZ), revealing a high sensitivity also at small momentum transfers. The two-triplon energy gap is found to be $100\pm 30$ meV. Our results are supported by calculations within an effective Hubbard model for a finite-size cluster.

cond-mat.str-el↗

arXiv2008

Dispersing bimagnons and doping induced bimagnon-charge modes in superconducting cuprates

In the early days of high temperature superconductivity it was already recognized that magnetic properties of these materials are intimately related to the superconducting ones . When doped, the long-range ordered antiferromagnetic background of pristine copper-oxide insulators melts away and makes room for a spin liquid and superconductivity. By resonant inelastic x-ray scattering (RIXS) in the soft regime we probe the hitherto inaccessible dynamical multiple-spin correlations of the magnetic background in a series of parent compounds and in high Tc materials [NCCO (Nd2-xCexCuO4) and LSCO (La2-xSrxCuO4)]. High resolution measurements allows the clear observation of dispersing bimagnon excitations. In the undoped compounds the theory, fits the data on these coherent spin excitations without free parameters. In nearly optimally doped LSCO we observe the appearance of a new collective excitation at an energy of 250 +/- 60 meV having the signature of a coupled bimagnon-charge mode. It has a strongly reduced dispersion and lies in a so far unexplored region of momentum and energy space in the mid-infrared.

cond-mat.str-el↗

arXiv2008

Evidence of orbital reconstruction at interfaces in La0.67Sr0.33MnO3 films

Electronic properties of transition metal oxides at interfaces are influenced by strain, electric polarization and oxygen diffusion. Linear dichroism (LD) x-ray absorption, diffraction, transport and magnetization on thin La0.7Sr0.3MnO3 films, allow identification of a peculiar universal interface effect. We report the LD signature of preferential 3d-eg(3z2-r2) occupation at the interface, suppressing the double exchange mechanism. This surface orbital reconstruction is opposite of that favored by residual strain and independent of dipolar fields, chemical nature of the substrate and capping.

cond-mat.str-el↗

arXiv2006

A determination of the pairing interaction in the high Tc cuprate superconductor Tl2Ba2CaCu2O8 (Tl2212)

We have measured the near-normal reflectance of Tl2Ba2CaCu2O8 (Tl2212) for energies from 0.1 to 4.0 eV at room temperature and used a Kramers-Kronig analysis to find the complex, frequency dependent dielectric function, from which the optical conductivity was determined. Using Thermal-Difference-Reflectance (TDR) Spectroscopy the reflectance of the sample in the normal state just above the superconducting transition, and in the superconducting state were then obtained. From these data we determined the ratio of the superconducting- to normal-state optical conductivities. Mattis and Bardeen had calculated this function within the BCS theory, where the gap is a fixed energy-independent quantity. Taking into account the retarded nature of the electron-phonon coupling results in a complex, energy dependent gap causing deviations from the Mattis-Bardeen plot at energies where the phonon coupling function is large. We find a typical deviation near the phonon energies in Tl2212, and in addition, at 1.2 and 1.7eV. The phonon, and these electronic terms can each be described by a coupling constant. None of which by itself gives rise to a high transition temperature, but the combination does. Using Resonant Inelastic X-Ray Scattering (RIXS) we find that the d-to-d excitations of the cuprate ion in Tl2212 fall at the same energies as the dips in the Mattis-Bardeen plot. We conclude that the high superconducting transition temperature of the cuprates is due to the sum of the phonon interaction, and interactions with the Cu-ion d-shell.

cond-mat.supr-con↗